1. Field of the Invention
The present invention relates to a display driver, an electro-optical device, and an electronic appliance.
2. Description of the Related Art
Display panels, as represented by LCD (Liquid Crystal Display) panels are mounted on mobile telephones and mobile information terminals (personal digital assistants or “PDAs”). LCD panels in particular can be made smaller, have lower power consumption, and can be produced at lower cost than other types of display panels, and thus are being installed into a variety of electronic appliances.
As one example, an LCD panel includes a plurality of common electrodes and a plurality of segment electrodes, and also a plurality of pixels that are specified by the common electrodes and the segment electrodes. The segment electrodes of the LCD panel are driven based on display data by a display driver. The common electrodes of the LCD panel are scanned by a scan driver.
Power consumption can be reduced by internally providing the display driver with a RAM that stores one frame of display data, for example. The display data is supplied to the display driver by a host, such as an external MPU (Micro Processor Unit).
The RAM is composed of a plurality of RAM cells, each of which is specified using a row address and a column address. A RAM cell stores image data for one dot that composes one pixel. This array of RAM cells corresponds to the array of pixels on the LCD panel. For this reason, the host supplies display data to the display driver in accordance with the orientation of the image to be displayed on the LCD panel. In the display driver, the display data from the host is written into RAM cells that are successively designated using row addresses and column addresses. After this, the display driver reads one frame of display data during one vertical scanning period and drives the LCD panel.
An image is generated at the host using the coordinate system defined on the LCD panel (for example, coordinate axes in two dimensions with a top-left pixel of the LCD panel as the origin). The display driver that drives the LCD panel has a coordinate system defined using row addresses and column addresses (for example, coordinate axes for two dimensions with a RAM cell with a row address “0” and a column address “0” as the origin) for designating individual cells in the plurality of RAM cells that compose the RAM provided inside the display driver. The positional relationship between the respective origins of these two coordinate systems changes depending on how the display driver is arranged relative to the LCD panel.
For this reason, display drivers have been designed so that the origin of the coordinate system defined for the internal RAM can be changed and the scanning direction can also be changed.
However, there has been the problem that it has been necessary for the host to calculate row addresses and column addresses, which designate RAM cells into which display data is to be written, in accordance with a mounting state of the display driver.
The present invention was conceived in view of the technical problem described above and it is an object of the present invention to provide a display driver, an electro-optical device, and an electronic appliance that do not need to perform a process for finding positions in a RAM into which display data is to be written in accordance with a mounting state thereof.